The production of oil and natural gas from an underground well (subterranean formation) can be stimulated by a technique called hydraulic fracturing, in which a viscous fluid composition (fracturing fluid) containing a suspended proppant (e.g., sand, bauxite) is introduced into an oil or gas well at a flow rate and a pressure which create or extend a fracture into the oil- or gas-containing formation. The proppant is carried into the fracture by the fluid composition and prevents closure of the formation after pressure is released. Leak-off of the fluid composition into the formation is limited by the composition's fluid viscosity. Fluid viscosity also permits suspension of the proppant in the composition during the fracturing operation. Cross-linking agents, such as borates, titanates or zirconates are usually incorporated into the composition to control viscosity.
Putzig, et al., in U.S. Pat. Nos. 4,808,739 and 4,885,103, disclose N,N-bis-(2-hydroxyethyl)glycine/metal chelates and their use in plugging permeable subterranean zones and leaks. In U.S. Pat. No. 4,996,336, Putzig, et al. disclose a process for preparing a metal chelate by reacting N,N-bis-(2-hydroxyethyl)-glycine (BHET) with a titanium halide, titanium oxyhalide, zirconium halide, zirconium oxyhalide, tetraalkyl zirconate, or a certain tetraalkoxy (2-hydroxy-ethyl)glycine/metal chelate.
BHET may be produced by a number of routes, including the condensation of ethylene oxide with glycine, the condensation of chloroacetic acid with diethanolamine, the hydrolysis of N,N-bis(2-hydroxyethyl)-acetonitrile, and the hydrolysis of 4-(2-hydroxyethyl)-2-morpholinone. BHET has a number of small-volume uses in the biological and research fields, applications for which a high purity is generally required. It is available commercially, but generally at a high price.
The condensation of chloroacetic acid with diethanolamine to produce BHET is described in Kromov-Borisov and Remizov, in Zhur. Obshchei Khim., 1953, 23, 598. Monochloroacetic acid was dissolved in water and neutralized with sodium hydroxide. The resulting solution of sodium monochloroacetate was added to diethanolamine and the mixture boiled and refluxed 3 to 4 hours. Khromov-Borisov and Remizov teach an extensive process comprising several steps to purify and isolate the product from the process solution. These steps are time-intensive and expensive. However, impurities, including unreacted starting materials and impurities generated in the process can interfere with formation and performance of a zirconium cross-linking agent prepared from the product of the process. For example, glycolic acid can be formed as a byproduct in the reaction by hydrolysis of chloroacetic acid or sodium chloroacetate. In some cases, this can be as high as 10–15%. Not only is there yield loss but also performance of the metal complex is adversely affected and made variable, depending on the extent and amount of impurities present, rather than consistent across batches of product. It is known that glycolic acid-based cross-linking agents result in a faster cross-linking rate than those based on BHET.
Gump, et al., in J. Org. Chem., 1959, 24, 712–14, disclose preparation of BHET using the process as described by Khromov-Borisov and Remizov, but added that: “In order to obtain satisfactory yields, refluxing of the mixture should be carried out for 24 hr. instead of 3 to 4 hr.”
There is a need for a process for making the zirconium or titanium salts of BHET without the above cumbersome, time-consuming and costly methods required for optimizing BHET yield, purification and isolation.